Embodiments of the present invention relate to a sputtering target for sputtering process chambers.
A sputtering chamber is used to sputter deposit material onto a substrate in the fabrication of integrated circuits and displays. Typically, the sputtering chamber comprises an enclosure around a sputtering target facing a substrate support, a process zone into which a process gas is introduced, a gas energizer to energize the process gas, and an exhaust port to exhaust and control the pressure of the process gas in the chamber. The sputtering target is bombarded by energetic ions formed in the energized gas causing material to be knocked off the target and deposited as a film on the substrate. The sputtering chamber can also have a magnetic field generator that shapes and confines a magnetic field about the target to improve sputtering of the target material. The sputtered target material may be a metal, such as for example aluminum, copper, tungsten, titanium, cobalt, nickel or tantalum. Elemental materials may be sputtered with inert gases such as argon or krypton and gases such as nitrogen or oxygen may be used to sputter elemental materials to form compounds such as tantalum nitride, tungsten nitride, titanium nitride or aluminum oxide.
However, in such sputtering processes, some portions of the target can be sputtered at higher sputtering rates than other portions resulting in the target exhibiting an uneven cross-sectional thickness or surface profile after processing a batch of substrates. Such uneven target sputtering can arise from variations in localized plasma density caused by the chamber geometry, the shape of the magnetic field about the target, eddy currents induced in the target, and other factors. Uneven sputtering can also be caused by differences in grain size or the structure of the surface material of the target. For example, it has been found that uneven target sputtering can result in the formation of concentric circular depressions at which material was sputtered from the target at higher rates than from surrounding areas. As the depressions get deeper, the chamber wall and backing plate behind the target become exposed and can be sputtered away resulting in contamination of the substrate with these materials. Also, a target having a variable non-uniform surface profile can result in deposition of uneven thicknesses of sputtered material across the substrate surface. Thus sputtered targets are typically removed from the chamber before any depressions formed on the target become too deep, wide or numerous. As a result, a large portion of the thickness of the sputtering target remains unused because the target has to be removed prematurely from the chamber.
It is desirable to have a sputtering target which can provide uniform sputtering for an extended sputtering time without requiring frequent replacement. It is also desirable to have a target which can be sputtered without excessive risk of erosion through its thickness. It is further desirable to have a sputtering target which provides uniform sputtering properties throughout its life.